Focusing drives of this kind are utilized, for example, in surgical microscopes of the Assignee for opthalmology, such as the LEICA M501, to move the microscope in the focusing direction in order to adjust the focus. The focusing drive comprises for this purpose a linear stroke carriage that carries the optics carrier (which in this case represents the microscope) and moves it in the focusing direction. An electrical drive is always used in these known focusing drives, which drive always requires an additional linkage to convert the rotary motion of the motor into the desired linear motion. This can involve, for example, a belt drive (e.g. toothed belt) or a gear combination, which move the linear stroke carriage in the focusing direction via a spindle. The motor and spindle are usually arranged next to one another parallel to the focusing direction, so that the focusing drive is correspondingly physically wide.
Greases are used to avoid wear; these help to limit friction as well as noise resulting therefrom.
The occasionally high rotation speeds of the drive motor and thus also of the gearing or linkage, however, produce noise that is usually loud and, in particular when a surgical microscope is being used, is unpleasant and irritating to the user. This noise results on the one hand from the elements themselves and on the other hand from the transfer of sound (especially through the usually thin-walled housing elements).
DC or stepping motors are obtainable exclusively without noise-damping features. Subsequent actions must therefore be taken to diminish noise.
The generally complex design of the known focusing drives, resulting from the aforesaid plurality of components that for the most part are not standard components and thus entail additional outlay for manufacture and assembly, proves to be disadvantageous. The use of ordinary drives (e.g. DC motors) requires additional linkage elements that convert the rotary motion of the motor into the desired linear motion of the focusing drive. Even when they correspond to a standard, these linkage elements require complex connecting structures such as bearing, attachment, and alignment systems, which then turn out to require service when considered over the working life of the product. The need to regrease or realign or readjust various linkage elements in order to obtain the desired functionality already represents a definite disadvantage for the user and the manufacturer.
The aforementioned noise output, which is unpleasant and irritating to the user, requires complex measures such as special bearing systems and casings, application of compounds or linings of housing parts (solid-borne sound), which nevertheless are often not sufficiently effective. This represents a further clear shortcoming of known focusing drives.